Light cured polymeric materials are widely used in the field of dentistry for adhesion, sealing and restoration, and may be cured or hardened upon exposure to a source of radiation. Such photoactive materials are cured generally when exposed to a specific radiation spectrum depending on the type of photoactivator being used, and most commonly, a photo-activated chemical reaction is initiated by the application of a high intensity blue light having a wavelength of 400-500 nanometer.
Photocurable dental materials are a convenience to the dentist as curing processes can be initiated when desired. For example, an amount of photocurable filling material is properly placed in a tooth cavity. A source of light next to the tooth cavity is then positioned proximate to the material and activated to initiate polymerization and subsequent curing of the composition to secure the repair.
The first generation of photocured dental materials were hardened by the application of concentrated beams of ultraviolet (UV) radiation. Apparatuses for producing concentrated beams of UV radiation are known from e.g. U.S. Pat. Nos. 4,112,335 and 4,229,658. Later, visible light curable dental materials were used and dental radiation guns for producing concentrated visible light were provided like that disclosed in U.S. Pat. No. 4,385,344. However, a relatively high divergence of about 25 degrees of the light beam from such visible light sources reduces penetration into the dental prosthesis material, leading to their relative inefficiency and unreliability for photo-curing dental materials that are thicker than about two millimeters.
Photocurable dental materials have also been developed that are hardened by exposure to radiant energy in a pre-selected spectral range. Typically, a photo-activated chemical reaction in many photo-curable dental materials is initiated by application of a high intensity blue light having a wavelength of 400-500 nanometers. Since the light sources employed typically produce the entire visible light spectrum as well as some non-visible radiation, a reflector is coated to reflect only visible light, and the filters are selected to substantially block non-visible radiation and visible light other than blue light in the range of 400-500 nanometers, in order to produce the desired range of radiation, as shown for example in U.S. Pat. No. 5,147,204.
A disadvantage of the curing apparatuses of the prior art discussed above is that the majority of the light produced by the curing apparatuses is in an ineffective wavelength, and consequently, most of the light supplied to the teeth is simply dissipated as heat. This is not desirable as the pulp in the teeth is very sensitive to heat.
Laser-based radiation sources have also been employed, using for example, a Nd YAG laser producing radiation at a wavelength of about 1060 nanometers, in combination with a frequency doubling material as disclosed for example in U.S. Pat. No. 5,885,082. In the instance that a laser source is used, the beam must be de-focused to cover the area being cured and this is done by varying by hand the distance between the dental composition and the laser dental gun.
More recently, LED light sources have been used to provide a high intensity light nearly exclusively in the effective wavelength, e.g. about 470 nanometers, as shown in for example U.S. Pat. No. 6,318,996, EP-1 090 608, and JP-2000-070292.
A disadvantage with these prior art curing lights is that the LEDs cannot effectively be brought close enough to the material to be cured in order to obtain a sufficient curing depth. Further, the tip of the light guides used is relatively small, so that only an area of about 0.3 cm2 can effectively be exposed to radiation. Thus, it is difficult to treat a larger dental prosthesis evenly.